This error indicates that the return type of mm is not supported by the R Snippet node. This function mm can either be used in the R View node to visualize the result or in the R Learner, the model can then be used in the R Predictor. For more details on the ecdf package please see http://stat.ethz.ch/R-manual/R-devel/library/stats/html/ecdf.html for an example: